Canon EX AUTO - Manual Control of Aperture

Manual Control of Aperture
Incoming light and depth-of-field can be manually controlled
by turning the aperture control ring to the direction of
"1.8-16". The exposure indicator in the viewfinder moves
to indicate the pre-set f/stop . Use this method when using
the flash
unit, photographing in counter-lighted situation,
or stressing high-key/low -key effects.
.. The diaphragm will close down to the pre-set f/stop
only for the instant that the shutter is released. Except
for that instant, the diaphragm remains fully open .
• As
the f/stop valu~ ~ts larger, the amount of iight reaching
the film plane becomes correspondingly less. For each f/stop
up, the light is reduced one-half. Accordingly, when the
aperture is increased by one f/stop, the exposure is doubled,
and when
it is increased by two f/stops the exppsure is
quadrupled.
• The
ratio between the aperture and the amount of exposure,
using
f/2 as the basis, is as follows :
f/stop :
1.8
ffi 2.8 3.5
Expo ur Ratio:
1. 25 1 1/2 1/3 1/4 1/8 1/16 1/32 1/64
4
5.6 8
11
16